Field of the Invention
This invention relates to a clock signal generating device and a clock signal generating method which are preferable in the case that data is reproduced in a magnetic disk, for example.
In the case that digital information recorded in disks such as a magnetic disk, an optical disk, an optomagnetic disk and the like is reproduced, or in the case that digital information is recorded in the disk, it becomes necessary to provide a clock which may become a reference value for a reproducing operation or a recording operation.
In a self-lock system which is commonly applied in a magnetic disk device, a clock component is already contained in the data itself, resulting in that a clock signal can be produced from reproduced data.
To the contrary, in a disk of so-called sampled servo system, clock marks are already formed on the disk at desired intervals and then a clock signal is produced through a PLL circuit in reference to a reproducing signal of each of the clock marks.
This reproducing clock signal can keep a quite precise synchronizing relation of about a value less than 10 ns in regard to a clock mark and then a recording or a reproducing of data synchronous with the reproducing clock signal synchronized with this clock mark can take place.
However, in the case that a power supply was turned on, for example, or in the case of a clock synchronization establishing process such as the cases in which a lock of a PLL circuit for use in producing the reproducing clock signal was released and a drawing operation was carried out again, there was a problem that there was a possibility that the reproducing head continued to run on the track having the recording data similar to the clock mark and the clock mark was frequently detected in an erroneous manner at this time, so that it took much time to perform a drawing of it into a correct clock mark.
The present invention has been invented in view of the aforesaid state and aims at an arrangement in which the clock signal can be produced rapidly and positively even at the time of establishing a clock synchronization.